As an exposure apparatus which exposes a substrate to a fine pattern of, for example, a semiconductor chip such as an IC or LSI, liquid crystal panel, CCD, thin-film magnetic head, micromachine, or the like, there is known a charged particle beam exposure apparatus which draws a pattern using an electron beam or ion beam, such as an electron beam exposure apparatus (see Japanese Patent Laid-Open No. 9-245708), ion beam exposure apparatus, or the like.
FIG. 5A shows a conventional raster scanning electron beam exposure apparatus. In FIG. 5A, reference symbol S denotes an electron source which emits an electron beam, and B, a blanker. An electron beam from the electron source S forms an image of the electron source S at the same position as the blanker B through an electron lens L1. The image of the electron source is reduced and projected onto a wafer W through a reduction electron optical system comprising electron lenses L2 and L3. The blanker B is an electrostatic deflector which is located at the same position as the image of the electron source S formed through the electron lens L1. The blanker B controls whether to irradiate the wafer with an electron beam. More specifically, when the wafer is not to be exposed to an electron beam, the blanker B deflects the electron beam, and a blanking aperture stop BA located on the pupil of the reduction electron optical system cuts off the deflected electron beam (i.e., an electron beam EBoff). On the other hand, when the wafer is to be exposed to an electron beam, an electron beam EBon having passed through the blanking aperture stop BA is controlled by an electrostatic deflector DEF to scan the wafer W.
A method of drawing on the wafer by raster scanning will be described with reference to FIG. 5B. For example, to draw a pattern of a character “A”, a drawing region is divided into a plurality of pixels. While the deflector DEF moves an electron beam to perform scanning in the X direction, the blanker B performs control such that each pixel constituting part of the pattern (gray portion) is irradiated with the electron beam and each of the remaining pixels shields the electron beam. When the scanning in the X direction ends, the electron beam is stepped in the Y direction, and the scanning in the X direction restarts. Electron beam irradiation is controlled during the scanning, thereby drawing the pattern.
As shown in FIG. 6A, when the blanker B switches the beam state from an electron beam OFF state to an electron beam ON state to irradiate the wafer W with an electron beam, the electron beam is made to move on the blanking aperture stop BA by the blanker B and passes through the aperture of the blanking aperture stop BA.
In the conventional apparatus, the diameter of electron beam is smaller than the aperture diameter of the blanking aperture stop, and a driver which drives the blanker B serving as the electrostatic deflector may cause an overshoot. For this reason, even in the beam ON state, the center of the electron beam fluctuates about the center of the aperture (d≠0) until it stabilizes at the center of the aperture, as shown in FIG. 6B. An image of an electron beam which comes incident on the wafer at a position shifted from the center of the aperture does not have a desired axisymmetric intensity distribution as shown in FIG. 6D but has a distorted intensity distribution as shown in FIG. 6C. Accordingly, it is difficult to form a desired fine pattern on the wafer.